www.bluemoment.com/emergencyrudders.html
is a reprint of the original Bob MacFarland article (without pics) that I ran into years ago.
www.pineapplesail.com (click 'articles') has very helpful actual installations with photos that might help developing the idea for the Ariel.

I've never seen photos of an emergency rudder in use.
The emergency rudder concept could be used to find out if a permanent transom hung rudder is feasible.